1. Field of the Invention
The present invention relates to a magnetic recording medium and a magnetic recording apparatus for recording magnetic data on the magnetic recording medium by applying a magnetic field and by heating.
2. Description of the Related Art
Conventionally, magnetic recording apparatus such as hard disks have been significantly improved in areal density, for example, by employing finer magnetic grains or alternative materials for the recording layer of magnetic recording media and advanced microprocessing for recording and reproducing heads. Further improvement in areal density is still being expected.
However, these conventional approaches to the improvement of areal density have already reached their limits due to several problems that have come to the surface. For example, the circumferential length of a recording bit may be reduced in order to increase the recording density in the circumferential direction of the track. Yet, this causes relatively great thermal fluctuations in the magnetic grains that constitute the recording layer, thereby making it difficult to sustain the recorded signals with stability.
In this context, there has been suggested a patterned medium as a candidate magnetic recording medium capable of providing further improved areal density. This patterned medium has a recording layer formed in a concavo-convex pattern in a data area and recording elements for recording magnetic data are formed of convex portions of the concavo-convex pattern. Furthermore, in each of tracks, the convex recording elements are separated from each other in a circumferential direction and arranged in a row in the circumferential direction.
Also suggested is using, as a material for the recording layer, one that has higher magnetic anisotropic energy and higher coercivity. For example, as a material for the recording layer, it is suggested to use a material having a coercivity as high as 4 kOe or greater.
However, in general, the recording magnetic field used for saturation magnetic recording is said to need a strength of about twice the coercivity. In some cases, use of the aforementioned material having high magnetic anisotropic energy and high coercivity for the recording layer would make it difficult for the conventional magnetic head to magnetically saturate the recording layer. That is, magnetic data could be recorded or erased with difficulty.
In contrast to this, a heat-assisted magnetic recording apparatus has also been suggested. This apparatus is designed to heat a portion of the recording layer by irradiating it with a beam of light and thus temporarily reduce coercivity of the portion. Then, a recording magnetic field is applied to this portion for recording magnetic data.
The heat-assisted magnetic recording apparatus employing the patterned medium will likely provide further improvement in areal density (for example, see Japanese Patent Application Laid-Open No. 2004-355739, No. 2007-73116, and No. 2008-34004).
However, in the recording layer, not only the portion irradiated with the beam of light but also its surrounding portions are heated by heat transfer. Also, the temperature distribution of the heated portion and magnetic field distribution of the magnetic head are not uniform. Furthermore, the magnetic recording medium rotates at high speed relative to the recording head and the heating head.
Thus, it was difficult to create a region where recording magnetic field is greater than the coercivity of the recording layer thereby magnetic data can be recorded or erased only at a target recording element of the magnetic recording medium in the same shape as that of the target recording element by use of the magnetic head and the heating head. Accordingly, in some cases, it was impossible to reliably record magnetic data on the target recording element entirely from one end to the other end. In particular, since the magnetic recording medium rotates at high speed relative to the magnetic head and the heating head, it was difficult to reliably record magnetic data on the target recording element from one end to the other end in the circumferential direction. Note that the region in which magnetic data is recordable and erasable may be created by the recording head and the heating head in a shape sufficiently greater than that of the target recording element on the magnetic recording medium. This may assure it to record the magnetic data on the target recording element from one end to the other end in the circumferential direction. However, in this case, it is likely that the magnetic data may also be accidentally recorded not only on the target recording element but also on other recording elements adjacent to the target recording element.